Commentaires 0

Retranscription du document

CHAPTER15—CENOZOICEVENTS

CHAPTER OVERVIEW

The Cenozoic Era is divided by most geologists into two periods: the Paleogene and the Neogene. This“newer” approach represents a move to an equal division of the epochs and also a more natural way ofdividing Cenozoic rocks in Europe. The Cenozoic, although covering only the last 66 million years,represents major worldwide changes. One such change occurred when the North Atlantic rift extended tothe north, separating Greenland from Scandinavia and thereby

destroying the land connection betweenEurope and North America. During the late Eocene epoch, Australia separated from Antarctica and thenbegan its journey to its present location. This is considered the only major continental breakup during theCenozoic; however, it appears to have affected climates around the world.

The stratigraphy of the Cenozoic of North America is explored with some of the more noteworthyexposures: the Gulf Coast, Rocky Mountains, High Plains, Basin and Range, Colorado Plateau,

ColumbiaPlateau and Cascades, Sierra Nevada, and California are discussed. The sedimentation and deformationof the Cenozoic outside North America is also discussed in order to complete this phase of Cenozoichistory. Pleistocene Glaciation is a focalpoint in this chapter which highlights the Glacial and Interglacialstages in North America and Europe as well as discussing variations in climatic conditions.

LEARNING OBJECTIVES

By reading and completing information within this chapter, you should gain an understanding of thefollowing concepts:



Sketch and label the Paleogene and Neogene Periods and the epochs within each.



Discuss the tectonic-climate connection.



Locate on a map the major mountain systems that were formed by the northward movingAfrican block as it collided with the underside of Europe.



Explain the origin of the following physiographic features of North America: RockyMountains/High Plains, Basin and Range, Colorado Plateau, Columbia Plateau andCascades, Sierra Nevada and California.



Describe the formation of the San Andreas Fault.



Explain the orogenic events along the Tethys seaway and the orogenic events that led to theformation of the Alps, Carpathian, Pyrenees, Apennines, and Himalayas.



Discuss the origin of Lake Molawi and Lake

Tanganyika in eastern Africa.



List the four Glacial/Interglacial Stages for North America and Europe from oldest to youngest.



Discuss the impacts of Pleistocene glaciation.



Explain the Milakovich Effect (Theory) and its possible interpretation of the PleistoceneGlaciation including the three variables in your explanation.

CHAPTER OUTLINE

I.

The Tectonic-Climate Connection

II.

Stability and Erosion Along the North American Margin

III.

Gulf Coast: Transgressing and Regressing Sea

IV.

Tectonics and Erosion in the Rockies

A.

Sediment and Mineral Wealth

B.

Remarkable Fossils

C.

Majestic Scenery

V.

Creating the Basin and Range Province

VI.

Colorado Plateau Uplift

Chapter 15—Cenozoic Events

VII.

Columbia Plateau and Cascades Volcanism

VIII.

Sierra Nevada and California

IX.

The New West Coast Tectonics

X.

Meanwhile, Drama Overseas

A.

Northern Europe

B.

Rifting Africa

C.

Semitropical Antarctica

XI.

Big Freeze: the Pleistocene Ice Age

A.

Pleistocene and Holocene Chronology

B.

Stratigraphy of Terrestrial Pleistocene Deposits

C.

Pleistocene Deep-Sea Sediments

D.

Many Impacts of Pleistocene Glaciation

1.

Shifting Sea Level

2.

Depressed Crust Rebounds

3.

Redirecting Mighty Rivers

4.

Forming Lakes, Great and Small

5.

Washington’s Alien Land: the Channeled Scablands

6.

Windblown Sediment

XII.

Why Did Earth’s Surface Cool?

A.

Milankovitch Cycles

B.

Earth’s Albedo

C.

Other Factors

XIII.

Cenozoic Climates

Chapter 15—Cenozoic Events

KEYTERMS

(Pages 451–485))

albedo (482):The fraction of solar energy reflected back into space is termed the Earth’salbedo.

channeled scablands (480):With the recession of the glacier, the ice dam broke, and tremendousfloods of water rushed out catastrophically across eastern Washington, causing severe erosion anddepositing huge volumes of gravel, boulders, and cobbles. The dissected region is appropriately termedthechanneled scablands. This event was associated with the formation ofPleistocene lakes in thenorthwestern corner of the United States.

discoaster (475):Calcareous, often star-shaped fossils believed to have been produced by golden-brown algae related to coccoliths.

kettle (479):A depression in glacial drift that is formed by the melting of a detached block of ice that wasburied in the drift.

Little Ice Age (476):The four-century period (AD 1540 and 1890) when temperatures were often 2 to 4°degrees Fahrenheit cooler than today in Europe and the United States.

loess

(480):Deposits of thick layers of windblown silt formed from fine-grained glacial sediments thathave been spread across outwash plains and floodplains by wind transportation.

The order of glacial stages/interglacial stages in the Pleistocene from oldest to youngest is

a.

Nebraskan, Kansan, Illinoian, Wisconsin.

c.

Nebraskan, Illinoian, Kansan, Nebraskan.

b.

Wisconsin, Illinoian, Kansan, Wisconsin.

d.

Wisconsin, Kansan, Illinoian, Nebraskan.

15.

G. Milankovich’s theory for Pleistocene Glaciation, which accounts for the Earth’s movements, isbased on three variables. The second variable refers to the way the axis of rotation moves slowly ina circle that is completed about every 26,000 years. It is called

a.

inclination.

c.

orbital spin.

b.

declination.

d.

precession.

16.

A period of cooler and drier climatic condition from 1540 to 1890 AD was called the

a.

Messinian event.

c.

“Little Ice Age.”

b.

Milankovich hypothesis.

d.

interglacial period.

17.

The overall global temperature of the Cenozoic started to decrease during what geologic period?

a.

Eocene

c.

Miocene

b.

Oligocene

d.

Pleistocene

18.

The best record of Cenozoic strata in North America is found in the _______________ where eighttransgressions and regressions are recorded.

a.

Colorado Plateau

c.

Gulf of Mexico Coastal Plain

b.

Cascade Range

d.

Atlantic Gulf Coast

19.

The Florissant Fossil Beds were produced during the _________________; it recorded the eruptionof volcanoes that produced ash that buried countless insects, leaves, spores, pollen, fish, and somebirds.

a.

Eocene

c.

Miocene

b.

Oligocene

d.

Pliocene

20.

Crustal movements began during the early _________________ that caused the elevation of theSierra Nevada along a great fault producing the Basin and Range Province.

a.

Eocene

c.

Paleogene

b.

Oligocene

d.

Neogene

Chapter 15—Cenozoic Events

FILL IN THEBLANK

1.

The western edge of North America during most of the Cenozoic was the site of an eastward-dipping subduction zone. The oceanic plate that was being fed into the subduction zone has beennamed

The most complete and best record of Cenozoic strata inNorth America is found on the

.

4.

The recent activity at Mount St. Helens and the older eruptions that gave rise to the volcanic peaksof the Cascades are the surface expression of the American plate and the

plate.

5.

These calcareous, often star-shaped fossils believed to have been produced by golden-brown algaerelated to coccoliths are called

.

6.

The basin that is not only a sedimentary basin, but a structural

basin as well and represents the typearea for most of the Cenozoic epochs is called

.

7.

The lakes that were particularly numerous in the northern part of the Basin and Range Province ofNorth America, where faulting produced more than 140 closed basins, were called

.

8.

The large scale physiographic province of the late Tertiary faulting that included portions of Nevada,Arizona, New Mexico and southern California was called

and

Province.

9.

West of the Columbia Plateau lies

an uplifted belt that was also the site of extensive volcanicactivity. It was further characterized by outpourings of more viscous lavas that resulted in whatmountains?

10.

The interfingering of permeable sands and impermeable clays provide ideal conditions for theeventual entrapment of oil and gas in what part of the Cenozoic Province of North America?

11.

During the Oligocene explosive volcanic activity in this area of Colorado produced a great deal ofash, which settled to the bottom of a neighboring lake, burying thousands of insects, leaves, fish,few birds, and trees. This area is called the

.

12.

The term used in Europe to describe dark, siliceous shales, poorly sorted sandstones, and chertsthat accumulated between elongated submarine banks is

.

13.

The best-known feature resulting from the linked processes of uplift and erosion on the ColoradoPlateau is

of the Colorado River.

14.

The sedimentary feature which consists of a thin, dark winter layer and a light-colored summer layerrepresenting the depositional record of

a single year is

.

15.

The Cenozoic Era is divided into two periods: the _________________ and the________________.

Chapter 15—Cenozoic Events

TRUE-FALSE

1.

The great thickness of sediment (10,000) that has accumulated during the Cenozoic inthe Gulf Coast and Gulf of Mexico indicates that the area experienced considerablesubsidence during deposition.

2.

For the most part, the Lower Tertiary sediments of the Rocky Mountain region consist ofgray siltstones, sandstones, carbonaceous shales, lignite, and coal.

3.

The Basin and Range Province occupies a broad zone from Nevada and Western Utahsouthward into Central Mexico.

4.

During the Miocene, the Columbia Plateau formed volcanic activity.

5.

Mount Kilimanjaro and Mount Kenya are isolated remnants of a great thrust sheet causedby the collision of India against eastern Africa.

6.

According to the plate tectonic hypothesis, the crustal compression that resulted in theformation of the Pyrenees and Atlas Mountains was the result of a collision betweennorthwestern Africa and southwestern Europe.

7.

A branch of the Indian Ocean opened between Arabia and Africa during the Cenozoic thatcreated the Gulf of

Aden and Red Sea.

8.

The Tethys Seaway of the Mesozoic was closed by plate tectonic collisions in theCenozoic.

9.

Lake Malaui and Lake Tanganyika, in eastern Africa, are the result of water accumulationin downfaultedblocks of crust formed during the current rifting activity in that region.

10.

The Himalayan Mountains formed as a result of the collision of India with Eurasia duringthe Cenozoic.

Chapter 15—Cenozoic Events

ANSWERKEY

Multiple Choice

1.

c

2.

c

3.

a

4.

b

5.

b

6.

d

7.

a

8.

d

9.

b

10.

a

11.

b

12.

b

13.

c

14.

a

15.

d

16.

c

17.

c

18.

c

19.

b

20.

d

Fill Ins

1.

farallon plate

2.

coal

3.

Gulf Coastal Plain

4.

Juan deFuca

5.

discoasters

6.

Paris basin

7.

pluvial lakes

8.

Basin, range

9.

cascade range

10.

Gulf Coastal Plain

11.

Florissant Flora

12.

flysch

13.

Grand Canyon

14.

Varves

15.

Paleogene

True/False

1.

T

2.

T

3.

T

4.

T

5.

F

6.

T

7.

T

8.

T

9.

T

10.

T

Chapter 15—Cenozoic Events

RESPONSES TO QUESTIONS ACCOMPANYING SELECTED FIGURES

FIGURE 15–1 (p. 453) Although not specifically mentioned in the chapter, one would surmise that fossilswould be the evidence for a milder Antarctic climate during the early Tertiary. Such evidence includesactual spore and pollen fossils from early Tertiary rocks in Antarctica. Before Antarctica separated fromAustralia, it was warmed by currents moving toward the continent from lower latitudes. With separation,cold polar currents entered the breach between the two landmasses, resulting in frigid conditions.

FIGURE 15–6 (p. 456) In order to accommodate 27,000 feet of sediment in a shallow depositional basin,the basin would have had to subside as it was being filled.

FIGURE A

(p. 461) Bedrock of impermeable clays and shales, the absence of a protective cover of plants,and infrequent heavy rains are the primary conditions under which badlands are formed.